The deployment of stents at a stenting site within a human or animal body requires careful handling of the stent delivery system to be used for deploying the stent. Exact positioning of the stent at the site of the stenosis prior to and during deployment is essential. The accuracy with which the stent can be deployed with respect to the occlusion inside the body lumen, as well as the skills of the surgeon in controlling the stent delivery system, will have an impact on the outcome of the operation.
Normally, a guidewire is used, to advance a stent delivery system containing the stent to be deployed into the body to the site of the stenosis. Once the distal end of the delivery system has reached the stenting site and the stent to be released is correctly located, the stent is released. To deploy a self-expanding stent it is known to gradually withdraw an outer sheath (otherwise called sleeve) holding the stent in a radially compressed configuration and thereby allow the stent to radially expand and to anchor itself inside the body lumen. In commercially available delivery systems, the stent is prevented by an inner catheter from moving proximally with the sleeve as it retreats proximally, and is held in a radially compressed state by a co-axially disposed outer sheath or sleeve enclosing the stent and the inner catheter. The relative axial positions of the inner catheter and the outer sleeve are varied by manipulation of the delivery system.
Since the stent as well as the stenosis are not directly visible to the surgeon performing the operation, the stent deployment procedure requires a visualisation procedure, usually the injection of a radiopaque fluid, in order to visualise the location of the stent inside the body lumen. The fluid is injected into an annular cavity between the inner catheter and the outer sheath. The position of the stent as well as the location of the stenosis itself can then be monitored from outside the patient's body by using X-ray imaging machines showing the images of radiopaque marker rings on the distal end of the delivery system and a reduced intensity image corresponding to the constricted volume of radiopaque fluid through the occluded site. This allows the surgeon/radiologist to find the location of the stenosis and place the stent with sufficient accuracy.
During the course of the delivery procedure, the radially compressed stent is held axially at a fixed position by a pusher surface of the inner catheter, which typically abuts the proximal end of the stent inside the outer sheath of the delivery system. The proximal movement of the outer sheath to release the stent exerts a proximally directed force onto the stent which urges the stent to move in the same way. The surgeon has to counteract this tendency of the stent to move proximally by applying an adequate, distally-directed force onto the pusher element in order to off-set the opposing forces and to thereby keep the position of the stent fixed.
Typically, the stent is mounted into the delivery system at a manufacturing site. Then, the entire assembly is sterilised and air-tightly packed in a specially designed sealed enclosure. During sterilisation and packaging, there is always the risk that the co-axial components of the assembly might move so that the outer sheath may be displaced with respect to the inner catheter. Consequently, the position of the stent might be changed during these steps prior to its placement.
Therefore, it would be desirable to have a delivery system with a fluid injection port which is protected against inadvertent or premature movement of the outer sheath relative to the stent but is still simple to use and economical to manufacture.